PHYSICS: Changing Constants?

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Science  02 Jul 2004:
Vol. 305, Issue 5680, pp. 19b
DOI: 10.1126/science.305.5680.19b

Students of physics are taught that the fundamental constants of physics remain, well, constant with respect to time. That is, the laws of physics—the strengths of fundamental interactions—cannot be adjusted simply to accommodate observations that are not consistent with these laws. However, measurements of heavy-element isotope ratios that span geological time scales (billions of years) have indicated that the strength of the electroweak interaction, which is the force responsible for holding nuclei and electrons together and for radioactive beta decay, has, in fact, changed ever so slightly over this period.

Researchers are conducting laboratory-based metrology experiments in order to ascertain whether the constants are changing and, if so, what the limits of these changes are. Fischer et al. have performed precision measurements of the 1S — 2S transition frequency in hydrogen and have found that if the fine structure constant does change with time, then it drifts by no more than 0.9 ± 2.9 parts in 1015 per year. Comparable precision measurements looking at the ratio of magnetic moments of cesium and rubidium atoms show that any drift in the ratio is limited to less than −0.5 ± 1.7 parts in 1015 per year. Although these are small numbers, absolute confirmation that the constants drift in value over time would have important implications for any theories that propose to bring together general relativity and quantum mechanics. — ISO

Phys. Rev. Lett. 92, 230802 (2004).

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